Duplex communication systems are methods of transmitting signals that allow two people or two parts to communicate with one another in opposite directions. Duplex communication systems are widely used in the area of telecommunications and especially in telephony and computer networking. Existing duplex wireless communication systems include half-duplex and full duplex types.
Existing half-duplex wireless communication systems provide for communication in two directions, but only in one direction at a time. Thus, while the transmitter is transmitting, the receiver must wait until the transmitter stops before transmitting. Such systems require significant latency periods.
Full-duplex (also known as double-duplex) systems are capable of transmitting and receiving data-carrying signals simultaneously. Such systems still require that the transmissions be separated in some way to enable the receivers to receive signals at the same time as transmissions are being made. Such separation may be achieved by two well-known methods: frequency separation using frequency division duplex (FDD) and time separation using time division duplex (TDD).
FDD systems include a transmission antenna and a reception antenna and operate using two independent, non-overlapping channels, one for transmitting and one for receiving. This method requires implementation of complex filters to separate the very weak received signal from the very strong transmission signal and to enable the receiver not to be unduly affected by the transmitter signal.
TDD systems are capable of transmitting in two directions, but use a single channel that alternates between transmitting and receiving. Thus the transmitter and receiver operate on the same frequency, but only in one direction at a time. TDD systems do not require two channels and frequency selective filters to separate the received signal from the transmission system. However, TDD systems require a guard interval that includes (1) the time required for the transmission to travel from the transmitter to the receiver and (2) the time required for the receiver to change from receive to transmit mode. Thus, TDD systems tend to introduce more overhead and more latency than protocols used with full-duplex operations and are not generally suitable for use over long distances.
Frequency spectrum is becoming an increasingly scarce resource, while technological progress, particularly in the area of 3G and 4G telecommunication systems and wireless internet services, has greatly increased the demand for wireless broadband. Both full-duplex and half-duplex wireless communication systems utilize the wireless channel(s) in only one direction at any given moment of time, therefore wasting spectrum. There is a growing need to optimize the use of available spectrum and to provide a method and apparatus that can achieve satisfactory performance for short, medium, and long distance communications and allows a full-duplex wireless system to operate on a single channel, i.e., to utilize the wireless channel in both directions at the same time, therefore doubling the spectral efficiency.
Different solutions have been proposed to solve this problem. However, these solutions either involve the use of extra components such as antennas or other processing components, which means added complexity and cost.